Add event_log_file to the example config

doc/fuss_manager.yaml.example

@@ -7,6 +7,7 @@ arpwatch_datafile: '/var/lib/arpwatch/arp.dat'
 dhcp_log_file: '/var/log/syslog'
 debug: False
 operation_log_file: '/var/log/fuss-manager/operations.log'
+event_log_file: '/var/log/fuss-manager/event.log'
 playbook_log_dir: '/var/log/fuss-manager/playbooks.log'
 disabled_sources: ()